1. Field of the Disclosure
This disclosure relates to a liquid crystal display device with improved picture quality, and a driving method thereof.
2. Description of the Related Art
As the information society grows, flat display devices capable of displaying information have been widely developed. These flat display devices include liquid crystal display (LCD) devices, organic electro-luminescence display (OLED) devices, plasma display devices, and field emission display devices. Among the above display devices, LCD devices have the advantages that they are light and small and provide a low power drive and a full color scheme. Accordingly, LCD devices have been widely used for mobile phones, navigation systems, portable computers, televisions and so on.
The LCD device controls the transmittance of a liquid crystal on a liquid crystal panel, thereby displaying a desired image. The LCD device generally displays an image in a hold type unlike the impulse type of the cathode ray tube (CRT) display device according to the related art. This results from the fact that its liquid crystal has a slow response time.
FIGS. 1A and 1B are graphic diagrams showing light density variations for time in the LCD device and the CRT display devices according to the related art. As shown in FIG. 1A, the related art CRT display device displays the image in the impulse type that the light density is discontinuously varied. Meanwhile, the related art LCD device displays in the hold type that the light density is continuously varied as shown in FIG. 1B. When a motion image changing every frame is displayed on the LCD device of the hold type, an object dragging phenomenon, i.e., a motion blur, is generated.
To address this matter, an LCD device of the impulse type has been proposed which forces the image not to be periodically displayed.
FIG. 2 is a graphic diagram showing data voltage variation for time in an LCD device of the impulse type. As shown in FIG. 2, the LCD device of the impulse type according to the related art divides one frame period into a display interval, actually displaying a desired image, and a non-display interval, not displaying any image. Also, the LCD device provides a desired data voltage in the display interval, but a black data voltage not displaying any image in the non-display interval. In this matter, since the black data voltage is applied in the non-display interval and no image is display during the non-display interval, the motion blur phenomenon can be prevented.
FIG. 3 is a block diagram showing an LCD device of the impulse type according to the related art. The LCD device of the impulse type according to the related art can selectively perform a normal driving mode without the black data and a black data driving mode with the black data.
Referring to FIG. 3, a timing controller 1 generates gate control signals for controlling a gate driver 3 and data control signals for driving a data driver 8. The data control signals include a driving mode control signal enabling either the normal driving mode or the black data driving mode to be performed.
The gate driver 3 applies a gate signal to a liquid crystal panel 9 in response to the gate control signals.
The data driver 8 converts red, green, and blue data (hereinafter, “RGB data”) into analog data voltages which are compensated with (or which reflect) a gamma value generated in a gamma generator 7. Also, the data driver 8 applies only the analog data voltages or alternately these together with a black data voltage to the liquid crystal panel 9, according to the driving mode control signal applied from the timing controller 1. More specifically, if the normal driving mode is designated by the driving mode control signal, only the analog data voltages are applied to the liquid crystal panel 9 during one frame period. On the contrary, when the driving mode control signal designates the black data driving mode, the analog data voltages are applied to the liquid crystal panel 9 in the display interval of one frame period and a black data voltage is applied to the liquid crystal panel 9 in the non-display interval of the frame period. The analog data voltage applied to the liquid crystal panel 9 is generated in such a manner as to reflect the gamma value without regard to the normal driving mode and the black data driving mode.
However, a liquid crystal included in the liquid crystal panel 9 has no time enough to respond to the analog data voltage applied in the display interval due to the affect of the black data voltage applied in the non-display interval in the black data driving mode. As such, brightness is deteriorated. Referring to experimental brightness variations along gray levels in the normal and black data driving modes, as shown in FIG. 5, it is evident that the level of brightness in the black data driving mode is entirely reduced in comparison with that in the normal driving mode.
On the other hand, the gamma generator 7 of the LCD device of the impulse type according to the related art includes a plurality of resistors R1 to Rn connected serially, as shown in FIG. 4. The gamma generator 7 provides divided voltages on nodes between the resistors R1˜Rn as gamma voltages GAMMA1 to GAMMAn-1.